Levels of NO2, a pollutant released by factories, power plants and vehicle exhausts, have risen by about 50% over China over the past decade due to economic growth, says the ESA, and levels are continuing to increase.

By comparison, concentrations of NO2 have remained steady or declined over industrial parts of the US and eastern Europe, ESA says.

Exposure to NO2 in large quantities is known to cause lung damage and respiratory problems.

The gas is also a major ingredient of smog, the ground-level pollutant typically caused by interaction between sunlight and traffic pollution.

The data was sent back by instruments aboard the ESA Earth-monitoring satellite Envisat under a joint research project, called the Dragon Programme, by European and Chinese scientists.

"China's nitrogen dioxide concentration varies according to season," says Professor John Burrows, a University of Bremen environmental physicist involved in the project.

"There is more in the winter as a result of differing emission patterns and meteorology.

"For example, more fuel is burned for heating, and nitrogen dioxide persists longer in the atmosphere at that less sunny time of year, lasting around a day rather than hours, as in the summer."